The goal of this research is the identification and characterization of genes involved in the process of mammalian cell growth. The study of these genes and their encoded proteins will likely provide new insights into the molecular events involved in (and controlling) normal and neoplastic growth and development. Basic questions to be addressed are: (1) how is the expression of these genes regulated, and (2) what are the biological activities and functions of these growth-related proteins? Several genes, expressed preferentially in growing cells, have been isolated from a cDNA library prepared from the poly A+ RNA present in serum-stimulated BALB/c 3T3 mouse tissue culture cells. This investigation will focus primarily on one of these genes, named proliferin because of its high level of expression in proliferating cells and its identification as a new member of the prolactin - growth hormone gene family. Analysis of this gene (and other growth-related genes) will include nucleotide sequencing of the genomic clone. These result will be utilized to examine the evolution of this important hormone gene family. Mutations will be introduced into the proliferin gene, and the effect of these changes will be evaluated in terms of gene expression in transfection assays. Additional effort will be directed towards expressing the proliferin gene in bacteria, purifying the protein from bacteria and from mouse cells (for testing hormone-like activities), and raising polyclonal antisera against proliferin. The antisera will be used to search for (1) the location of proliferin within a cell, (2) the presence of the protein in specific cells and tissues, and (3) the synthesis of proliferin at defined times and stages of murine development and differentiation; attempts will also be made to block proliferin activity with these antisera. The proliferin genomic and cDNA clones, inserted into eukaryotic expression vectors, will be reintroduced into mouse cells to monitor the activity of the newly synthesized proliferin protein in relation to cell growth. Further expansion of the collection of growing cell-specific genes will enable future research towards a more complete view of the process of cell growth.